Gasoline, alcohol, such as ethanol or methanol, and blended fuel of gasoline and alcohol are used as fuel for an internal combustion engine. JP-2007-9903A (WO-2006/129198A1) and JP-2007-146831A (US-2007/009533A1) show a fuel injection controller which estimates alcohol concentration of the fuel and corrects fuel injection quantity based on the estimated alcohol concentration.
Generally, cleaning agent is added to gasoline. As the alcohol concentration of the fuel increases, the function of the cleaning agent is deteriorated. When the alcohol fuel, such as alcohol or blended fuel, is used as fuel, deposit is easily accumulated at a vicinity of an injection port of a fuel injector. Hence, in a case that the alcohol fuel is used as the fuel, even if the fuel injection is corrected according to the alcohol concentration, when the accumulated deposit quantity is increased, a fuel injection characteristic of the fuel injector is varied, so that the fuel injection quantity deviates from a proper value. Thus, an exhaust emission and a drivability may be deteriorated.
However, in the conventional system, since the deposit quantity accumulated on the fuel injector can not be detected, an appropriate process is not performed promptly when the deposit quantity is increased.